Crude resumed flowing on Sunday after 9,120 barrels of oil leaked out in North Dakota in late October, marking Keystone's largest-ever spill. Pipeline operator TC Energy (NYSE:TRP) said the line will now operate it at a reduced pressure, gradually increasing the volume of crude moving through the system. Users of the pipeline are also concerned that Keystone's transportation exemption - for higher than standard pressure levels - may be at risk after four significant leaks over the past decade.